Much attention is being given to the use of liquid crystal display devices in large screen televisions. When compared with existing notebook personal computers and liquid crystal monitors, the performance required of large liquid crystal display televisions is becoming increasingly exacting in terms of stability with respect to changes in angle of vision, contrast and the environment in which the device is used. Accordingly, the polarizing plate used in the liquid crystal display device, and the cellulose ester film used in the polarizing plate are subjected to the same exacting requirements in terms of performance, and because the stretched cellulose ester film greatly affects optical performance, this is an important member and there are strict requirements in terms of the specifications.
One property which has been subjected to exacting requirements due to use in large screen televisions is humidity stability of optical properties, and because existing cellulose ester films are highly hygroscopic, there has been a problem in that humidity stability is poor.
The inventors discovered that by including specific polyesters in the cellulose ester, the humidity stability of the optical properties was improved. Up until the present time, there have been a number of proposals with respect to including polyester in the cellulose ester (see Patent Documents 1-4 for example). However, the proposal that have been made up until now, do not suggest improvement of humidity stability of the optical properties to begin with, and furthermore, in almost all of these proposals, when an amount of 10% or less is included, cloudiness and bleeding out occurs and thus improvement was desired urgently.
[Patent Document 1] Unexamined Japanese Patent Application Publication No. (referred to as JP-A) 2002-22956
[Patent Document 2] JP-A 2002-267846
[Patent Document 3] JP-A 2004-175971
[Patent Document 4] JP-A 2004-175972